Cracking the Coding: Practice Problem

main.java

// ch 8.7
import java.util.*;

public class Main {
    public static void main(String args[]) {
        System.out.println(getPerms("ab"));   // [ab, ba]
        System.out.println(getPerms("abc"));  // [abc, acb, bac, bca, cab, cba]
        System.out.println(getPerms("love")); // [love, loev, lvoe, lveo, leov, levo, olve, olev, ovle, ovel, oelv, oevl, vloe, vleo, vole, voel, velo, veol, elov, elvo, eolv, eovl, evlo, evol]
    }
    static ArrayList < String > getPerms(String input) {
        ArrayList < String > perms = new ArrayList < > ();
        if (input.length() == 0) {
            perms.add(input);
        } else {
            for (int i = 0; i < input.length(); i++) {
                ArrayList < String > sub = getPerms(input.substring(0, i) + input.substring(i + 1, input.length()));
                for (String s: sub) {
                    perms.add(input.charAt(i) + s);
                }
            }
        }
        return perms;
    }
}
// ch 8.13
import java.util.*;

public class Main {
    public static void main(String args[]) {
        System.out.println("Hello");
        ArrayList<Box> boxes = new ArrayList<>();
        boxes.add(new Box(1, 1, 1));
        boxes.add(new Box(2, 2, 2));
        boxes.add(new Box(3, 3, 3));
        System.out.println(createStack(boxes)); // 6
        boxes.add(new Box(3, 4, 3));
        System.out.println(createStack(boxes)); // 7
        boxes.add(new Box(6, 4, 4));
        boxes.add(new Box(7, 5, 5));
        boxes.add(new Box(7, 7, 7));
        System.out.println(createStack(boxes)); // 17
    }
    static class Box implements Comparable<Box> {
        int w, h, d;
        
        Box(int w, int h, int d) {
            this.w = w;
            this.h = h;
            this.d = d;
        }        
        public int compareTo(Box b) {
            if (this.w < b.w && this.h < b.h && this.d < b.d) return -1;
            if (this.w > b.w && this.h > b.h && this.d > b.d) return  1;
            return 0;
        }
    }
    static int createStack(ArrayList<Box> boxes) {
        int maxheight = 0;
        for (Box b: boxes)
            maxheight = Math.max(maxheight, createStack(b, boxes));
        return maxheight;
    }
    static int createStack(Box bottom, ArrayList<Box> boxes) {
        int maxheight = 0;
        for (Box b: boxes)
            if (bottom.compareTo(b) > 0)
                maxheight = Math.max(maxheight, createStack(b, boxes));
        return bottom.h + maxheight;
    }
}
// ch 13.8
import java.util.*;
import java.util.stream.*;

public class Main {
    public static void main(String args[]) {
        List<Integer> list = new ArrayList<>();
        list.add(1);
        list.add(2);
        list.add(3);
        list.add(4);
        list.add(5);
        
        System.out.println(getRandomSubset(list));
    }
    static List<Integer> getRandomSubset(List<Integer> list) {
        Random random = new Random();
        return list.stream().filter(k -> random.nextBoolean())
                            .collect(Collectors.toList());
    }
}
// 16.7: Number Max
import java.util.*;
public class Main {
    public static void main(String args[]) {
        System.out.println(getMax(10000, 10001)); // 10001
    }
    static int getMax(int a, int b) {
        int sum = a + b;
        int dff = Math.abs(a - b);
        int min = (sum - dff) / 2;
        return sum - min;
    }
}